scholarly journals Effects of the High-Order Ionospheric Delay on GPS-Based Tropospheric Parameter Estimations in Turkey

2020 ◽  
Vol 12 (21) ◽  
pp. 3569
Author(s):  
Volkan Akgul ◽  
Gokhan Gurbuz ◽  
Senol Hakan Kutoglu ◽  
Shuanggen Jin
Keyword(s):  
Solar Activity ◽  
High Order ◽  
Ionospheric Delay ◽  
High Solar Activity ◽  
Tropospheric Delay ◽  
Parameter Estimations ◽  
The North ◽  
Gps Processing ◽  
Tropospheric Delays ◽  
Gps Observations

The tropospheric delay and gradients can be estimated using Global Positioning System (GPS) observations after removing the ionospheric delay, which has been widely used for atmospheric studies and forecasting. However, high-order ionospheric (HOI) delays are generally ignored in GPS processing to estimate atmospheric parameters. In this study, HOI effects on GPS-estimated tropospheric delay and gradients are investigated from two weeks of GPS data in June 2011 at selected GPS stations in Turkey. Results show that HOI effects are up to 6 mm on zenith tropospheric delay (ZTD), 4 mm on the North-South (NS) gradient and 12 mm on the East-West (EW) gradient during this period, but can reach over 30 mm in slant tropospheric delays. Furthermore, the HOI effects on tropospheric delay and gradient are larger in the daytime than the nighttime. Furthermore, HOI effects on tropospheric delay are further investigated on low and high solar activity days. The HOI effects on GPS estimated tropospheric delay and gradients in high solar activity days are higher than those in low solar activity days.

scholarly journals The Effects of Higher-Order Ionospheric Terms on GPS Tropospheric Delay and Gradient Estimates

2018 ◽  
Vol 10 (10) ◽  
pp. 1561 ◽  
Author(s):  
Zhiyu Zhang ◽  
Fei Guo ◽  
Xiaohong Zhang
Keyword(s):  
Geomagnetic Storms ◽  
Satellite System ◽  
High Elevation ◽  
Higher Order ◽  
Ionospheric Delay ◽  
Gradient Estimates ◽  
Tropospheric Delay ◽  
The North ◽  
Global Navigation Satellite ◽  
The Impact

Atmospheric delays, e.g., ionospheric delay and tropospheric delay, are the dominant error sources for the Global Navigation Satellite System (GNSS), especially for Precise Point Positioning (PPP). The common method for eliminating ionospheric delay is to form an ionosphere-free (IF) observable, which is a linear combination of observables on two frequencies such as GPS L1 and L2. As for the tropospheric delay, the dry component can be precisely corrected by empirical models, while the wet component is usually estimated as unknowns. However, the higher-order ionospheric (HOI) terms are not totally cancelled out in the (first-order) IF observable and as such, when not accounted for, they degrade the accuracy of other parameters. The impact of HOI corrections is well documented in the literature. This paper investigates the temporal effects of HOI terms on estimated tropospheric parameters, i.e., zenith tropospheric wet delay (ZWD) and north and east gradients. For this purpose, observations from over 100 stations with good global coverage were used considering various geographic and geophysical conditions. The results of numerical experiments show that HOI effects have a significant impact on the estimated tropospheric parameters, and the influence is dependent on location and time. The maximum differences of ZWD estimates reach over 20 mm during periods of activity such as solar storms and geomagnetic storms. Additionally, the north gradients are more likely to be affected by HOI effects compared with east gradients. In particular, the tropospheric gradient component is most affected for low latitude station during daytime. Additionally, the effects of bending errors and HOI terms on slant tropospheric delay at low elevation angles are much larger than those at high elevation angles.

scholarly journals The influence of solar activity on action centres of atmospheric circulation in North Atlantic

2015 ◽  
Vol 33 (2) ◽  
pp. 207-215 ◽  
Author(s):  
L. Sfîcă ◽  
M. Voiculescu ◽  
R. Huth
Keyword(s):  
Solar Activity ◽  
Sea Level ◽  
North Atlantic ◽  
High Solar Activity ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. We analyse the response of sea level pressure and mid-tropospheric (500 hPa) geopotential heights to variations in solar activity. We concentrate on the Northern Hemisphere and North Atlantic in the period 1948–2012. Composite and correlation analyses point to a strengthening of the North Atlantic Oscillation and weakening (i.e. becoming more zonal) of the Pacific/North American pattern. The locations of points with lowest and highest sea level pressure in the North Atlantic change their positions between low and high solar activity.

Statistical investigations of polar patch occurrence during high solar activity

2021 ◽  
Author(s):  
Rafal Sieradzki ◽  
Jacek Paziewski
Keyword(s):  
Solar Activity ◽  
Large Scale ◽  
Density Ratio ◽  
Coupled System ◽  
High Solar Activity ◽  
Seasonal Effect ◽  
Polar Regions ◽  
The North ◽  
Background Density ◽  
A Tec

<p>The circumpolar ionosphere is recognised as one of the most disturbed region of the ionized part of the atmosphere. The reasons for that are mainly dynamic conditions in the coupled system of the magnetosphere and the ionosphere as well as feeding of the polar plasma from the mid-latitude reservoir. One of the consequences of these phenomenon is the occurrence of large-scale ionospheric structures called polar patches. These are commonly defined as the enhancement of the F-region plasma characterized with a foreground-to-background density ratio larger than 2 and a size up to several hundred kilometres.</p><p>In this work we present GNSS-based characteristics of a patch occurrence in the northern hemisphere. The study covers a period of January–May 2014 corresponding to the maximum of the solar activity. The detection of structures was performed with a relative STEC value that is defined as a difference between epoch-wise L4 data and 4<sup>th</sup> order polynomial corresponding to background variations of the ionosphere. In order to ensure a continuous monitoring of the ionosphere over the north pole, we used data from ~45 permanent stations. The results prove that ground-based GNSS data can be successfully used in the climatological investigations of polar patches. We found a strong seasonal effect in the occurrence of these structures with the maximum at the turn of February and March and the minimum in May. Such outcomes correspond to variations of a TEC gradient between subauroral and polar regions. This parameter seems to be also responsible for a subdaily pattern of patches observed for particular months. The comparison of GNSS-based results with in-situ SWARM data revealed some differences, which are probably related to different characteristics of the ionosphere provided by both techniques. Furthermore, the study confirms that most of the patches are observed for the negative values of IMF Bz,  whereas IMF By component has no significant impact on the number of analysed structures. </p>

The effect of multi-GNSS and ionospheric delay on real-time velocity estimation with the variometric approach

2020 ◽  
Author(s):  
Tao Geng ◽  
Zhihui Ding
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Real Time ◽  
Sunspot Number ◽  
Seismic Velocity ◽  
Vertical Component ◽  
Velocity Estimation ◽  
Ionospheric Delay ◽  
High Solar Activity ◽  
Variometric Approach

<p>The variometric approach, based on time difference technique in which single-receiver code and carrier phase observations are processed along with available broadcast orbits and clocks, presents a high accuracy on estimating receiver velocity (at mm/s level) in real time. In order to analyze the effect of ionospheric delay on velocity estimation, we evaluate the velocity estimation accuracy of six selected stations with different latitude at approximately 120-degree longitudes during a solar cycle from 2009 to 2019. Compared with the low-solar activity year, velocity estimation RMS during the high-solar activity year will increase by 2-4 mm/s in the east, north and up direction. Velocity estimation RMS time series agree well with the sunspot number time series. The correlation coefficients of six stations between RMS values and sunspot number are 0.45-0.66, 0.39-0.52, 0.39-0.63 in the east, north and up direction respectively. The accuracy of velocity estimation is positively correlated with the sunspot number. We also reconstructed seismic velocity waveforms caused by the 2017 Mw 6.5 Jiuzhaigou earthquake using variometric approach. The results show that multi-GNSS fusion can improve the velocity accuracy by 1-2 mm/s in the horizontal component and 3-4 mm/s in vertical component, with an improvement of 47%, 54%, 41% in the east, north, up direction compared with GPS-only results.</p>

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

2021 ◽  
Vol 44 ◽  
pp. 85-91
Author(s):  
V.N. Obridko ◽  
◽  
D.D. Sokoloff ◽  
V.V. Pipin ◽  
A.S. Shibalova ◽  
...  
Keyword(s):  
Solar Activity ◽  
Activity Cycle ◽  
Solar Interior ◽  
Local Fields ◽  
Lower Atmosphere ◽  
High Solar Activity ◽  
Dynamo Model ◽  
Sunspot Activity ◽  
Geomagnetic Variations ◽  
Near Surface

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

Periodicities in the north-south asymmetry of solar activity

Solar Physics ◽  
1989 ◽  
Vol 119 (2) ◽  
pp. 411-414 ◽  
Author(s):  
G. Vizoso ◽  
J. L. Ballester
Keyword(s):  
Solar Activity ◽  
The North ◽  
South Asymmetry

scholarly journals Regularity of the north-south asymmetry of solar activity

2002 ◽  
Vol 383 (2) ◽  
pp. 648-652 ◽  
Author(s):  
K. J. Li ◽  
J. X. Wang ◽  
S. Y. Xiong ◽  
H. F. Liang ◽  
H. S. Yun ◽  
...  
Keyword(s):  
Solar Activity ◽  
The North ◽  
South Asymmetry

scholarly journals A Neural Network-Based TEC Model Capable of Reproducing Nighttime Winter Anomaly

2021 ◽  
Vol 13 (22) ◽  
pp. 4559
Author(s):  
Marjolijn Adolfs ◽  
Mohammed Mainul Hoque
Keyword(s):  
Neural Network ◽  
Solar Activity ◽  
Geomagnetic Latitude ◽  
Machine Learning Techniques ◽  
High Solar Activity ◽  
Electron Content ◽  
Solar Cycles ◽  
Total Electron ◽  
The Neural Network ◽  
Winter Anomaly

With the availability of fast computing machines, as well as the advancement of machine learning techniques and Big Data algorithms, the development of a more sophisticated total electron content (TEC) model featuring the Nighttime Winter Anomaly (NWA) and other effects is possible and is presented here. The NWA is visible in the Northern Hemisphere for the American sector and in the Southern Hemisphere for the Asian longitude sector under solar minimum conditions. During the NWA, the mean ionization level is found to be higher in the winter nights compared to the summer nights. The approach proposed here is a fully connected neural network (NN) model trained with Global Ionosphere Maps (GIMs) data from the last two solar cycles. The day of year, universal time, geographic longitude, geomagnetic latitude, solar zenith angle, and solar activity proxy, F10.7, were used as the input parameters for the model. The model was tested with independent TEC datasets from the years 2015 and 2020, representing high solar activity (HSA) and low solar activity (LSA) conditions. Our investigation shows that the root mean squared (RMS) deviations are in the order of 6 and 2.5 TEC units during HSA and LSA period, respectively. Additionally, NN model results were compared with another model, the Neustrelitz TEC Model (NTCM). We found that the neural network model outperformed the NTCM by approximately 1 TEC unit. More importantly, the NN model can reproduce the evolution of the NWA effect during low solar activity, whereas the NTCM model cannot reproduce such effect in the TEC variation.

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